i make things

December 5, 2012March 1, 2017

Simple Button, Complex Design

I pulled apart my car’s start/stop button today to redo some chipping paint that was bothering me. Naturally, I couldn’t stop at only the cosmetic plastic once I saw that there was a small PCB inside. There are two interesting things about this picture. First, look at the PCB: there are some electronics (and more than just regulators to drive the LED), an LED to illuminate the button, and nothing else. Note: no metal contacts. In the button assembly, there’s a big white diffuser between the LED and front button face. I can only conclude that this means they’re using the LED itself to sense the amount of reflected light to detect a button press. It’s not revolutionary science, but it’s interesting that they chose a completely non-mechanical sense mechanism.

The other thing that’s interesting, and more visible in the view below, is the piece of silver trim that outlines the button. It’s definitely metal. Plinks like metal, feels like metal, looks like metal, and the acid test: scratches like metal. Yet look at the manufacturing lines on the back and inside. It’s almost certainly been injection molded! It certainly seems like we’re dealing with Liquidmetal here! Neat! (On second glance, it actually looks like it’s just really nicely metallized plastic – there’s metal there, but only skin deep.

you could mask off the lettering and re-spray paint the area, but then you’ll get an ugly paint line. I’d look into sanding the whole thing down to opaque, and see if you can find a vinyl sticker online somewhere to replace the lettering mask.